Anti-corrosive coating composition and process for formation of anti-corrosive coatings

ABSTRACT

Disclosed is an anti-corrosive coating composition comprising (a) 100 parts by weight of an unsaturated polyester resin, (b) 10 to 100 parts by weight of a glass flake having an average thickness of 0.5 to 5 microns and an average particle size of 100 to 400 microns, or 10 to 70 parts by weight of said glass flake and 10 to 150 parts of scaly metal pigment, (c) 0.1 to 1.0 part by weight of a ketone peroxide and (d) 0.5 to 2.0 parts by weight of a hydroperoxide and/or a peroxy ester. Also disclosed is a process for forming anti-corrosive coatings, which comprises spray-coating the above anti-corrosive coating composition to a thickness of 300 to 1500 microns by using a spray gun having a spray tip diameter of 0.5 to 3 mm.

This is a division of application Ser. No. 201,606, filed Oct. 28, 1980,now U.S. Pat. No. 4,363,889.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an anti-corrosive coating compositionproviding a tough coating excellent in corrosion resistance on an ironor steel substrate, and also to a process for forming such a coating byusing this anti-corrosive coating composition.

2. Description of the Prior Art

Resin linings for preventing corrosion and rusting of metals have beenused for various pollution-preventing apparatuses and chemicalapparatuses and also for tanks, oil tanks of ships and ship bottoms.

From the viewpoint of the normal temperature curing property in situoperation adaptability and the manufacturing cost, unsaturated polyesterresins have heretofore been used for formation of these resin linings.As the lining process, there has ordinarily been adopted the so-calledFRP lining process in which an organic peroxide is incorporated inadvance into a resin, a sheet-like substrate composed of glass fibers isapplied to a material to be lined, the sheet-like substrate isimpregnated with the resin by using a felt roll or the like and theresin is cured while simultaneously effecting defoaming.

In addition to this FRP lining process, the so-called flake liningprocess, which comprises coating a composition comprising a resin and avery thin flake composed of a vitreous substance onto a material to becoated by using a trowel has recently attracted attention in the art andhas already been put into practice.

As the composition that is used for practising this process, there areknown, for example, a protective or decorative coating compositioncomprising fine glass slices incorporated in an organic resin bindervehicle (see Japanese Patent Publication No. 25368/76) and a liningmaterial formed by filling a lining resin with a glass flake as ananti-corrosive substance and a glass fiber as a reinforcer (see JapanesePatent Application Laid-Open Specification No. 30855/77). Furthermore,there is known a plastic material, paint or insulating paper filled withglass scale which has been rendered hydrophobic or provided with aleafing property by surface treatment with an appropriate material (seeJapanese Patent Publication No. 16821/72).

In view of properties of the resulting coatings or films, all of theseknown compositions are applied to a very great thickness exceeding 2 mmso that the coating operation becomes very expensive. Accordingly, thesecompositions have only rarely been applied to ordinary steel structuresbut are used only for very limited purposes such as mentioned above.

If a flake lining now available is used in the form of a film having athickness of less than 2 mm with a view to reducing the cost, it isimpossible to impart the intended properties to the resulting coatingfilm, and hence, such film cannot be put into practical use.

In the above-mentioned composition including glass flakes, in order toeffectively exploit the characteristics of glass flakes and control thepermeation of corrosive ions by the glass flakes, how to arrange theglass flakes in parallel with the surface of a substrate is a veryimportant problem. In the conventional flake lining process using acoating composition including glass flakes, parallel arrangement of theglass flakes is promoted by levelling the coated surface with a trowelor roller. However, the running cost is increased if such trowel orroller is used, and this process cannot be applied to a structure havinga complicated configuration.

As means for eliminating these difficulties involved in the coatingoperation, there has been proposed a process using a glassflake-containing composition that can be sprayed. For example, there isknown a process for forming a polyester laminate, which comprisesspraying the surface of a metal with a slow gelling composition preparedby (1) mixing from 30 to 95% by weight, based on the composition, of apolyester resin, from 15 to 50% by weight, based on the composition, ofa cross-linking agent and up to 50% by weight, based on the composition,of glass, (2) adding to the mixture prepared in step (1) a productobtained by reacting from 0.1 to 0.5% by weight, based on thecomposition, of pentanedione with from 0.5 to 1.5% by weight, based onthe composition, of a metallic promotor and (3) adding about 1% byweight, based on the composition, of a catalyst capable of generatingfree radicals to the mixture of step (2) (see U.S. Pat. No. 3,653,954).However, even if spray coating is carried out by using theabove-mentioned composition, glass flakes are not arranged in parallelwith the surface of a substrate and deviation of the parallelarrangement according to the coating direction (horizontal plane andvertical plane) is large. Accordingly, manifestation of the effect ofglass flakes for controlling permeation of corrosive ions can hardly beexpected.

As is seen from the foregoing illustration, a coating process or coatingcomposition ensuring substantially parallel arrangement of glass flakesto the surface of a substrate has not been known. In particular, whenthe coating composition is applied in the form of a thin film, rustingis readily caused from pinholes, resulting in serious defects. Morespecifically, rust formed on pinholes grows rapidly, and rusting is notlimited in the pinhole portion but propagates to the interface betweenthe film and the iron or steel substrate, with the result that suchdefects as blistering and peeling appear.

SUMMARY OF THE INVENTION

It is therefore a primary object of the present invention to eliminatethe foregoing defects involved in the conventional techniques andprovide an anti-corrosive coating composition which is characterized inthat when the composition is spray-coated, glass flakes containedtherein can be arranged substantially in parallel with the surface of asubstrate to be coated, whereby a durable coating excellent in corrosionresistance, adhesion, impact resistance and weatherability is obtainedand a coating process using this anti-corrosive coating composition.

In accordance with one aspect of the present invention, there isprovided an anti-corrosive coating composition comprising 100 parts byweight of an unsaturated polyester resin, 10 to 100 parts by weight ofglass flake having an average thickness of 0.5 to 5 microns and anaverage particle size of 100 to 400 microns, 0.1 to 1.0 part by weightof a ketone peroxide and 0.5 to 2.0 parts by weight of a hydroperoxideand/or a peroxy ester.

In accordance with another aspect of the present invention, there isprovided an anti-corrosive coating composition comprising 100 parts byweight of an unsaturated polyester resin, 10 to 70 parts by weight of aglass flake having an average thickness of 0.5 to 5 microns and anaverage particle size of 100 to 400 microns, 10 to 150 parts by weightof a scaly metal pigment, 0.1 to 1.0 part by weight of a ketone peroxideand 0.5 to 2.0 parts by weight of a hydroperoxide and/or a peroxy ester.

In accordance with still another aspect of the present invention, thereis provided a process for forming anti-corrosive coatings, whichcomprises spray-coating in a coating thickness of 200 to 1500 microns acomposition comprising (a) 100 parts by weight of an unsaturatedpolyester resin, (b) 10 to 100 parts by weight of a glass flake havingan average thickness of 0.5 to 5 microns and an average particle size of100 to 400 microns, or 10 to 70 parts by weight of said glass flake and10 to 150 parts by weight of scaly metal pigment, (c) 0.1 to 1.0 partsby weight of a ketone peroxide and (d) 0.5 to 2.0 parts by weight of ahydroperoxide and/or a peroxy ester by using a spray gun having a spraytip diameter of 0.5 to 3 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron microscope photograph of a section of thecoating obtained in Example 1.

FIG. 2 is an enlarged photograph of a portion of the coating shown inFIG. 1.

FIG. 3 is a scanning electron microscope photograph of the coatingobtained in Comparative Example 1.

FIG. 4 is a scanning electron microscope photograph of a section of thecoating obtained in Example 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to an anti-corrosive coating compositionfor forming a tough coating excellent in corrosion resistance on an ironor steel substrate, and a coating process using this anti-corrosivecoating composition.

More specifically, the present invention relates to an anti-corrosivecoating composition comprising (a) 100 parts by weight of an unsaturatedpolyester resin, (b) 10 to 100 parts by weight of glass flake having anaverage thickness of 0.5 to 5 microns and an average particle size of100 to 400 microns, or 10 to 70 parts by weight of said glass flake and10 to 150 parts by weight of a scaly metal pigment, (c) 0.1 to 1.0 partsby weight of a ketone peroxide and (d) 0.5 to 2.0 parts by weight of ahydroperoxide and/or a peroxy ester.

An unsaturated polyester resin which is liquid at normal temperatureswithout dilution with a volatile solvent and which is cured by a curingagent or catalyst to provide a cured coating excellent in waterresistance and chemical resistance is preferably used as the unsaturatedpolyester resin in the present invention.

All of known unsaturated polyester resins can be used equivalently inthe present invention. These unsaturated polyester resins can besynthesized by carrying out an esterification reaction of an unsaturatedacid and a saturated acid with a polyhydric alcohol in an inert gasatmosphere and diluting the esterification product with a solvent orpolymerizable monomer. As the unsaturated acid and saturated acid, therecan be mentioned maleic anhydride, fumaric acid, citraconic aciditaconic acid, tetrachlorophthalic anhydride, Het acid,tetrabromophthalic anhydride, phthalic anhydride, isophthalic acid,terephthalic acid, endomethylene-tetrahydrophthalic anhydride,tetrahydrophthalic acid, hexahydrophthalic anhydride, succinic acid,adipic acid, azelaic acid, sebacic acid, anthrathene-maleic anhydrideadduct and rosin-maleic anhydride adduct. These acids may be used singlyor in the form of a mixture of two or more of them.

As the polyhydric alcohol to be reacted with the saturated acid andunsaturated acid, there can be mentioned ethylene glycol, diethyleneglycol, triethylene glycol, propylene glycol, dipropylene glycol,butane-diol-1,3, butane-diol-1,4, butane-diol-2,3, pentane-diol-1,5,hexane-diol-1,6, neopentyl glycol, 2,2,4-trimethylpentane-diol-1,3,hydrogenated bisphenol A, 2,2-di(4-hydroxypropoxyphenyl)propane,glycerin, pentaerythritol, diallyl ether, trimethylene glycol,2-ethyl-1,3-hexane-diol, trimethylol propane,cyclohexane-dimethanol-1,4, 2,2,4-tetramethylcyclobutane-diol-1,3,1,4-bis(2-hydroxyethoxy)benzene and2,2,4,4-tetramethylcyclobutane-diol-1,3. These polyhydric alcohols maybe used singly or in the form of a mixture of two or more of them.

Furthermore, polyester resins obtained by reacting an epoxy resin withan α,β-monoethylenically unsaturated monocarboxylic acid in the presenceof a reaction catalyst, if necessary with a polymerization inhibitor,can be used in the present invention.

The epoxy resin that is used for this reaction is a resin having atleast two epoxy groups in one molecule. As such epoxy resin, there canbe mentioned (1) an epoxy resin synthesized by reacting bisphenol A withepichlorohydrin or methylepichlorohydrin, (2) an epoxy resin synthesizedby reacting a glycol with epichlorohydrin or methylepichlorohydrin, (3)an epoxy resin synthesized by reacting a phenol with formaldehyde in thepresence of an acidic or alkaline catalyst and reacting the resultingnovolak or cresol compound with epichlorohydrin ormethylepichlorohydrin, (4) an epoxy resin synthesized by oxidizingintramolecular double bonds, (5) an epoxy resin synthesized by reactinga halogenated phenol with epichlorohydrin or methylepichlorohydrin, (6)an epoxy resin synthesized by adding ethylene oxide or propylene oxideto a phenol and reacting the resulting adduct with epichlorohydrin ormethylepichlorohydrin, and (7) an epoxy resin synthesized by reacting acarboxylic acid with epichlorohydrin or methylepichlorohydrin. Theseepoxy resins may be used singly or in the form of a mixture of two ormore of them.

It must be noted that epoxy compounds that can easily be anticipatedfrom the foregoing epoxy resins, and derivatives of these epoxy resins,can be similarly used in the present invention. For example, polyol typeepoxy resins, alicyclic epoxy resins and halogen-containing epoxy resinscan also be used in the present invention.

As the unsaturated monocarboxylic acid to be reacted with the epoxyresin, there can be mentioned, for example, acrylic acid, methacrylicacid and crotonic acid. Furthermore, monoesters of unsaturatedpolycarboxylic acids and monoesters of maleic acid can be used. Theseacids and monoesters may be used singly or in the form of a mixture oftwo or more of them.

As the reaction catalyst, there can be mentioned amines such astriethylamine and quaternary ammonium salts such as tetramethyl ammoniumchloride.

As the polymerization inhibitor, there can be mentioned, for example,hydroquinone, mono-t-butylhydroquinone, p-t-butylcathechol,2,5-di-t-butylhydroquinone, benzoquinone and2,5-diphenyl-p-benzoquinone.

As the polymerizable monomer, there can be mentioned, for example,styrene, vinyltoluene, divinylbenzene, vinyl acetate, methacrylic acid,methyl methacrylate, acrylic acid, ethyl acrylate, acrylonitrile,methacrylonitrile, ethylene glycol dimethacrylate, trimethylol propanetrimethacrylate, diethylene glycol bisallylcarbonate, diallyl phthalate,2,5-dichlorostyrene, diallyl ether, triallyl cyanurate,4-vinylcyclohexanone monoepoxide, vinylpyrrolidone and triallylphosphate. These monomers can be used singly or in the form of a mixtureof two or more of them.

As the solvent, there can be used, for example, aliphatic hydrocarbonsolvents, aromatic hydrocarbon solvents, halogenated hydrocarbonsolvents, alcoholic solvents, ketone type solvents, ester type solvents,ether type solvents, ketone-alcohol type solvents, ether-alcohol typesolvents, ketone-ether type solvents, ketone-ester solvents andester-ether type solvents. These solvents can be used singly or in theform of a mixture of two or more of them.

The foregoing polyester resins are ordinarily marketed as unsaturatedpolyester resin in the form of a composition containing about 10 toabout 50% by weight of an α,β-ethylenically unsaturated monomer having ahigh dissolving power, such as styrene or methyl methacrylate.Accordingly, the unsaturated polyester resin referred to in the presentinvention contains such monomer.

The glass flake that is used in the present invention is in the form ofvitreous, very thin, scaly particles having an average thickness of 0.5to 5 microns, preferably 1 to 3 microns, and an average particle size of100 to 400 microns, preferably 150 to 300 microns.

In the present invention, the glass flake is laminated in a plurality oflayers in the coating in parallel to the substrate, and serves toincrease the strength of the resin and, simultaneously, to preventpermeation and transmission of ambient materials such as vapor andwater. This preventive effect is ordinarily enhanced when the thicknessof the glass flake is small and the diameter is large. This tendency isconspicuous in a highly corrosive atmosphere or environment.

However, if the thickness of the glass flake is smaller than 0.5 micron,the strength of the glass flake is low and the glass flake cannot beused in practice. On the other hand, if the thickness of the glass flakeis larger than 5 microns, the glass flake is seldom arranged in parallelwith the substrate. Furthermore, if the size of the glass flake issmaller than 100 microns, the glass flake is soldom arranged in parallelwith the substrate, and the strength and corrosion resistance of thecoating cannot easily be improved. If the size of the glass flakeexceeds 400 microns, the adaptability of the coating composition to thespray-coating operation is reduced and use of a glass flake having sucha large size is not preferred.

From the viewpoint of the corrosion resistance and physical propertiesof the coating, it is preferred that the glass flake be incorporated inan amount of 10 to 100 parts by weight, especially 20 to 70 parts byweight, per 100 parts by weight of the unsaturated polyester resin(inclusive of styrene or the like as pointed out hereinbefore).

When the amount of the glass flake is smaller than 10 parts by weightper 100 parts by weight of the resin, the intended corrosion resistancecannot be obtained. On the other hand, when the amount of the glassflake exceeds 100 parts by weight per 100 parts by weight of the resin,the flexibility of the coating film is reduced and the coating filmbecomes brittle. Therefore, good results cannot be obtained.

In the present invention, methylethyl ketone peroxide is preferably usedas the ketone peroxide.

As the hydroperoxide that is used in the present invention, there can bementioned, for example, t-butyl hydroperoxide, cumene hydroperoxide,diisopropylbenzone hydroperoxide, p-methane hydroperoxide and2,5-dimethyl-2,5-dihydroperoxyhexane. Among these hydroperoxides, cumenehydroperoxide and t-butyl hydroperoxide are especially preferred. Thesehydroperoxides may be used singly or in the form of a mixture of two ormore of them.

As the peroxy ester, there can be mentioned, for example, t-butylperoxyphthalate, t-butyl peroxybenzoate, t-butyl peroxylaurate, t-butylperoxy-2-hexanoate, t-butyl peroxypivalate, t-butyl peroxyacetate andt-butyl peroxyisobutyrate. Among these peroxy esters, t-butylperoxyphthalate and t-butyl peroxylaurate are especially preferred.These peroxy esters may be used singly or in the form of a mixture oftwo or more of them.

In the present invention, by using the ketone peroxide in combinationwith the hydroperoxide and/or the peroxy ester, the pot life of thecoating composition, that is, the curing time of the coating, can becontrolled. Accordingly, in the present invention, parallel arrangementof the glass flake in the coating is effectively advanced afterspraying, and layers of the glass flake arranged in parallel with thesubstrate can be formed.

The amounts added of the ketone peroxide and the hydroperoxide and/orthe peroxy ester are appropriately determined while the above-mentionedeffect is taken into account. Namely, the amounts added of thesecompounds are readily influenced by the ambient temperature at thecoating step.

It was confirmed from the results of our experiments that the ketoneperoxide is preferably incorporated in an amount of about 0.6 part byweight at an atmospheric temperature of 5° C., about 0.3 part by weightat an atmospheric temperature of 20° C. or about 0.1 part by weight atan atmospheric temperature of 30° C., per 100 parts by weight of theunsaturated polyester resin solid (inclusive of styrene or the like). Italso was found that the hydroperoxide and/or the peroxy ester ispreferably incorporated in an amount of about 1.4 parts by weight at anatmospheric temperature of 5° C., about 0.7 part by weight at anatmospheric temperature of 20° C. or about 0.9 part by weight at anatmospheric temperature of 30° C., per 100 parts by weight of theunsaturated polyester solid. If the amounts of these compounds exceedthe above-mentioned levels at the respective atmospheric temperatures,the pot life is shortened and the coating operation becomes difficult,and since the coating cures completely is in a short time, there islittle parallel arrangement of the glass flake. On the other hand, ifthe amounts of the compounds are smaller than the above-mentionedlevels, the drying time becomes too long.

In the present invention, it is indispensable that the ketone peroxidebe used in combination with the hydroperoxide and/or the peroxy ester.The former compound makes contributions to the radical reaction of theunsaturated polyester resin, but if this compound alone is used, thespeed of the curing reaction is promoted to too great a degree, andparallel arrangement of the glass flake can hardly be attained.Accordingly, in order to control the radical reaction at normaltemperatures, this compound is used in combination with thehydroperoxide and/or the peroxy ester, whereby parallel arrangement ofthe glass flake is advantageously promoted.

In the composition of the present invention, in order to promotedecomposition of the above-mentioned peroxides, it is preferred that atleast one curing promoter selected from metal salts of naphthenic acid,such as cobalt naphthenate, manganese naphthenate, copper naphthenate,calcium naphthenate, barium naphthenate, zinc naphthenate and zirconiumnaphthenate be added in an amount of 0.3 to 1.5 parts by weight per 100parts by weight of the unsaturated polyester resin.

In accordance with another embodiment of the present invention, scalymetal pigment is incorporated together with the above-mentioned glassflake. In the composition of this embodiment of the present invention,by synergistic effects of the three components, that is, the unsaturatedpolyester resin, the glass flake and the scaly metal pigment, thedefects of the conventional resin linings can be eliminated, and acoating film excellent in corrosion resistance, adhesion andweatherability can be obtained.

More specifically, by lamination of the glass flake and scaly metalpigment, the effect of preventing permeation of corrosive ions can beenhanced, and furthermore, the corrosive ions react with the scaly metalpigment and they are converted to harmless substances before they reachthe metal substrate. Attainment of these effects of preventingpermeation of the corrosive ions and sequestering the corrosive ions isdue to the fact that the pigment is scaly. Furthermore, when the scalymetal pigment is used, the ductility possessed by the metal is given tothe coating film and hence, the flexibility of the coating film isimproved. This effect is especially important for improving poorphysical properties of a thick coating.

A scaly metal pigment which is stable in the unsaturated polyester resinis preferably used in the present invention. For example, there arepreferably employed scaly lead powder, scaly zinc powder, scalystainless steel powder, scaly aluminum powder and scaly copper powder. Ascaly anti-corrosive pigment represented by scaly lead powder and scalyzinc powder having a high anti-corrosive action to metals is especiallypreferred. It is preferred that the average particle size of the scalymetal pigment be 30 to 300 microns, especially 50 to 250 microns, andthe average thickness be 3 to 10 microns, especially 4 to 7 microns.

When the average particle size of the metal pigment is smaller than 30microns, the pigment is not substantially scaly and attainment of theeffect of preventing permeation of corrosive ions in the coating canhardly be expected. On the other hand, if the average particle size ofthe scaly metal pigment exceeds 300 microns, the pigment receives theviscous resistance of the resin in the coating, with the result thatparallel arrangement of the pigment is hard to attain, or that thestrength of the pigment per se is reduced. Accordingly, in this case, atthe paint-preparing step (kneading step) or the coating step, thepigment is readily bent or broken and the pigment is no longer scaly.Therefore, the intended objects of the present invention cannot beattained.

Furthermore, when a coating composition comprising a metal pigmenthaving an average particle size exceeding 300 microns is spray-coated,the spray tip is readily clogged with the metal pigment and the coatingoperation efficiency is reduced. Accordingly, use of such metal pigmentis not preferred.

It is ordinarily preferred that the scaly metal pigment be used in anamount of 10 to 150 parts by weight, especially 15 to 90 parts byweight, per 100 parts by weight of the unsaturated polyester resin.

If the amount of the scaly metal pigment is smaller than 10 parts byweight per 100 parts by weight of the unsaturated polyester resin, thetoughness, flexibility and corrosion resistance are reduced, and if theamount of the scaly metal pigment is larger than 150 parts by weight per100 parts by weight of the unsaturated polyester resin, the coating filmbecomes brittle. Accordingly, it is not preferred to use the scaly metalpigment in too large an amount or too small an amount.

In this embodiment where the above-mentioned scaly metal pigment isused, the glass flake is used in an amount of 10 to 70 parts by weight,preferably 20 to 60 parts by weight, per 100 parts by weight of theunsaturated polyester resin (inclusive of styrene or the like). If theglass flake is used in an amount included in this range, the corrosionresistance and physical properties of the coating are improved.

More specifically, if the amount of the glass flake is smaller than 10parts by weight per 100 parts by weight of the unsaturated polyesterresin, the intended corrosion resistance cannot be obtained, and if theamount of the glass flake is larger than 70 parts by weight of theunsaturated polyester resin, the flexibility is reduced and the coatingbecomes brittle. Accordingly, in each case, good results cannot beobtained.

In the above-mentioned coating composition of the present invention,additives such as curing promotors, coloring pigments, extenderpigments, anti-corrosive pigments, precipitation-inhibiting agents,dispersants, diluents and other scaly pigments may be incorporated,according to need.

The anti-corrosive composition of the present invention is obtained bymixing the unsaturated polyester resin, the glass flake and, accordingto need, the scaly metal pigment and other additives such as a curingpromotor, other pigments and the like according to a customary methodusing a disperser or the like, and adding as the curing agent the ketoneperoxide and the hydroperoxide and/or the peroxy ester at the time ofapplication.

In the present invention, the so obtained anti-corrosive composition iscoated on a substrate to be coated according to the spray-coatingmethod. Compressed air spray and airless spray are suitable as thespray-coating method. In case of the compressed air spray, an airpressure of at least 4 Kg/cm² is preferred, and in case of an airlessspray, a primary air pressure of at least 5 Kg/cm² and a compressionratio of at least 30/1 are preferred. It is preferred that the spray tipdiameter be 0.5 to 3 mm, especially 0.75 to 2 mm. If the spray tipdiameter is smaller than 0.5 mm, the tip is clogged with the glass flakeand it becomes impossible to perform the coating operation smoothly. Incontrast, if the tip diameter is larger than 3 mm, the spray pattern isnot expanded in a good condition.

In the coating process of the present invention, the coating compositionis coated on the substrate in a dry coating film thickness of 300 to1500 microns, preferably 500 to 1200 microns, according to theabove-mentioned coating procedures. If the coating thickness is smallerthan 300 microns, the corrosion resistance of the coating is reduced andparallel arrangement of the glass flake in the coating is hard toattain, so that good results cannot be obtained. If the thickness of thecoating is larger than 1500 microns, sagging is caused and no goodcoating is obtained. After the coating operation, the applied coatingcomposition is dried at normal temperatures and the intended coating isformed.

As is apparent from the foregoing illustration, if the specific coatingcomposition is spray-coated under specific conditions, the glass flakeand scaly metal pigment are arranged in the coating in parallel to thesubstrate. Accordingly, there can be obtained a coating excellent incorrosion resistance, chemical resistance, weatherability, adhesion andstrength.

If desired, a topcoat paint composed of a chlorinated rubber, an alkydresin, an epoxy resin, an urethane resin or an acrylic resin or atopcoat paint comprising an unsaturated polyester resin and glass flakemay be coated on the coating formed according to the present invention.The coating obtained according to the present invention has also anexcellent adhesion to such topcoat paint.

The present invention will now be described with reference to thefollowing Examples and Comparative Examples that by no means limit thescope of the invention.

EXAMPLE 1

    ______________________________________                                        Formula 1:                                                                    ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                        37     parts by weight                                   (Rigolac 150 HR manufactured by                                               Showa High Polymer Co. Ltd.:                                                  Isophthalic acid type)                                                        Organic bentonite (Bentone #34                                                                     2.0    parts by weight                                   manufactured by National Lead                                                 Co. Ltd.)                                                                     Styrene              35.5   parts by weight                                   Cobalt naphthenate (containing                                                                     0.5    part by weight                                    6% of metallic cobalt)                                                        Glass flake (average particle                                                                      15     parts by weight                                   size = 200 microns, average                                                   thickness = 2-3 microns)                                                      Talc                 5      parts by weight                                   Titanium oxide       5      parts by weight                                   Total                100    parts by weight                                   Curing agents:                                                                Methylethyl ketone peroxide                                                                        0.1    part by weight                                    Cumene hydroperoxide 0.3    part by weight                                    ______________________________________                                    

Among the main ingredients of formula 1, the unsaturated polyester resinwas first mixed with the organic bentonite and the mixture was kneadedby a roller. The remaining main ingredients were added to the mixture,and the mixture was stirred with a disperser to form a main ingredientcomposition. A soft steel plate (JIS G-3141) having a size of 150 mm×50mm×1.6 mm was subjected to shot blasting to remove will scale, rust andoil completely. The main ingredient composition of formula 1 in whichthe curing agents had been incorporated was coated on this steel plateto a dry coating thickness of 500±50 microns by compressed air spraing(tip diameter=1 mm). The coating was dried at 20° C. for 7 days, and thecoated steel plate was subjected to comparison tests.

Photographs of the section of the coating obtained in Example 1, takenby using a scanning electron microscope, are shown in FIGS. 1 and 2 forreference.

EXAMPLE 2

    ______________________________________                                        Formula 2:                                                                    ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                         40     parts by weight                                  (Rigolac LP-1 manufactured by                                                 Showa High Polymer Co., Ltd.:                                                 Bisphenol type)                                                               Organic bentonite (same as used                                                                     3.0    parts by weight                                  in Example 1)                                                                 Paraffin wax          0.3    part by weight                                   Styrene               11.2   parts by weight                                  Cobalt naphthenate (same as                                                                         0.5    part by weight                                   used in Example 1)                                                            Glass flake (same as used in Example 1)                                                             25     parts by weight                                  Talc                  15     parts by weight                                  Titanium oxide        5      parts by weight                                  Total                 100    parts by weight                                  Curing agents:                                                                Methylethyl ketone peroxide                                                                         0.15   part by weight                                   t-Butyl peroxyphthalate                                                                             0.3    part by weight                                   ______________________________________                                    

A coating composition of formula 2, formed by kneading in the samemanner as described in Example 1, was coated on the same type of steelplate sample used in Example 1, and the coated steel plate was subjectedto comparison tests.

EXAMPLE 3

    ______________________________________                                        Formula 3:                                                                    ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                        50     parts by weight                                   (Repoxy R-800 manufactured by                                                 Showa High Polymer Co., Ltd.:                                                 Epoxy acrylate type)                                                          Organic bentonite (same as                                                                         1.0    part by weight                                    in Example 1)                                                                 Paraffin wax         0.3    part by weight                                    Styrene              23.2   parts by weight                                   Cobalt naphthenate (same as                                                                        0.5    part by weight                                    in Example 1)                                                                 Glass flake (same as in                                                                            20     parts by weight                                   Example 1)                                                                    Titanium oxide       5      parts by weight                                   Total                100    parts by weight                                   Curing agents:                                                                Methylethyl ketone peroxide                                                                        0.3    part by weight                                    t-Butyl peroxyphthalate                                                                            0.7    part by weight                                    ______________________________________                                    

A composition of recipe formula 3, which was formed by kneading in thesame manner as described in Example 1 was airless-spray-coated on thesame type of steel plate sample as used in Example 1, so that the drycoating thickness was 500±50 microns (the tip diameter was 1 mm). Thecoated steel plate was dried at 5° C. and subjected to comparison tests.

EXAMPLE 4

    ______________________________________                                        Formula 4:                                                                    ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                        40     parts by weight                                   (UPICA 5523 manufactured by                                                   Japan U.PICA Co. Ltd.:                                                        Isophtalic acid type)                                                         Organic bentonite (Bentone #34                                                                     2.0    parts by weight                                   manufactured by National Lead                                                 Co. Ltd.)                                                                     Styrene              20     parts by weight                                   Cobalt naphthenate (containing                                                                     0.5    part by weight                                    6% of metallic cobalt)                                                        Glass flake (same as used in                                                                       20     parts by weight                                   Example 1)                                                                    Talc                 10     parts by weight                                   Titanium oxide       7.5    parts by weight                                   Total                100    parts by weight                                   Curing agents:                                                                Methylethyl ketone peroxide                                                                        0.2    part by weight                                    Cumene hydroperoxide 0.5    part by weight                                    ______________________________________                                    

A coating composition of formula 4, formed by kneading in the samemanner as in Example 1, was coated on the same type of steel platesample as used in Example 1 and the coated steel plate was subjected tocomparison tests.

EXAMPLE 5

    ______________________________________                                        Formula 5:                                                                    ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                        45     parts by weight                                   (Atlac 382-05 manufactured by                                                 Kao = Atlas Co. Ltd.: Bisphenol                                               type)                                                                         Organic bentonite (same as                                                                         2.0    parts by weight                                   used in Example 1)                                                            Paraffin wax         0.3    part by weight                                    Styrene              19.7   parts by weight                                   Cobalt naphthenate (same as                                                                        0.5    part by weight                                    used in Example 1)                                                            Glass flake (same as used in                                                                       20     parts by weight                                   Example 1)                                                                    Talc                 7      parts by weight                                   Titanium oxide       5.5    parts by weight                                   Total                100    parts by weight                                   Curing agents:                                                                Methylethyl ketone peroxide                                                                        0.1    part by weight                                    t-Butyl peroxyphthalate                                                                            0.4    part by weight                                    ______________________________________                                    

A coating composition of formula 5, formed by kneading in the samemanner as in Example 1, was coated on the same type of steel platesample as used in Example 1, and the coated steel plate was subjected tocomparison tests.

COMPARATIVE EXAMPLE 1

    ______________________________________                                        Formula 6:                                                                    ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                       50     parts by weight                                    (same as used in Example 1)                                                   Organic bentonite (same as                                                                        2.5    parts by weight                                    used in Example 1)                                                            Styrene             26.7   parts by weight                                    Cobalt naphthenate (same as                                                                       0.8    part by weight                                     used in Example 1)                                                            Glass flake (average particle                                                                     20     parts by weight                                    size = 40 microns, average                                                    thickness = 2-3 microns)                                                      Total               100    parts by weight                                    Curing agent:                                                                 Methylethyl ketone peroxide                                                                       1.5    parts by weight                                    ______________________________________                                    

A coating composition of formula 6 was air-spray-coated on the same typeof steel plate sample as used in Example 1 so that the dry coatingthickness was 500±50 microns. The coated sample was dried at roomtemperature for 7 days and subjected to comparison tests.

For reference, a photograph of the section of the so obtained coatingtaken by using a scanning electron microscope is shown in FIG. 3.

COMPARATIVE EXAMPLE 2

    ______________________________________                                        Formula 7:                                                                    ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                       45     parts by weight                                    (same as used in Example 1)                                                   Organic bentonite (same as                                                                        2.5    parts by weight                                    used in Example 1)                                                            Styrene             21.7   parts by weight                                    Cobalt naphthenate (same as                                                                       0.8    part by weight                                     used in Example 1)                                                            Glass flake (same as used                                                                         30     parts by weight                                    in Example 1)                                                                 Total               100    parts by weight                                    Curing agent:                                                                 t-Butyl peroxybenzoate                                                                            2.0    parts by weight                                    ______________________________________                                    

A coating composition of recipe 7 was air-spray-coated on the same typeof steel plate sample as used in Example 1 so that the dry coatingthickness was 500±50 microns, and the coated steel plate was dried atroom temperature for 7 days and subjected to comparison tests.

COMPARATIVE EXAMPLE 3

    ______________________________________                                        Formula 8:                                                                    ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                        45.0   parts by weight                                   (same as used in Example 1)                                                   Titanium white       1.0    part by weight                                    Thixotropic agent (powdery silica)                                                                 2.0    parts by weight                                   Paraffin wax (air releasing agent)                                                                 0.06   part by weight                                    Styrene              25.86  parts by weight                                   Glass flake (same as used                                                                          25.0   parts by weight                                   in Example 1)                                                                 Propylene glycol     0.68   part by weight                                    Cobalt tallate       0.2    part by weight                                    Pentane dione        0.2    part by weight                                    Total                100    parts by weight                                   Curing agent:                                                                 t-Butyl peroxybenzoate                                                                             1.0    part by weight                                    ______________________________________                                    

A coating composition of formula 8 was air-spray-coated on the same typeof steel plate sample as used in Example 1 so that the dry coatingthickness was 500±50 microns, and the coated steel plate was dried atroom temperature for 7 days and subjected to comparison tests.

The results of the comparison tests made on coatings formed in theforegoing Examples and Comparative Examples are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                  Example                                                                       1        Example 2 Example 3                                                                             Example 4                                ______________________________________                                        Salt spray                                                                              no       no change no change                                                                             no change                                resistance                                                                              change                                                              test.sup.1                                                                    Adhesion test                                                                           65       60        63      60                                       (Kg/cm.sup.2).sup.2                                                           Weather resis-                                                                          no       no change no change                                                                             no change                                tance test.sup.3                                                                        change                                                              Service water                                                                           29 days  30 days   35 days 40 days                                  dip resis-                                                                    tance test.sup.4                                                              Alkali resis-                                                                           no       no change no change                                                                             no change                                tance test.sup.5                                                                        change                                                              Acid resis-                                                                             no       "         "       "                                        tance test.sup.6                                                                        change                                                              Humidity resis-                                                                         no       "         "       "                                        tance test.sup.7                                                                        change                                                              Impact resis-                                                                           no       "         "       "                                        tance test.sup.8                                                              ______________________________________                                                           Compara-  Compara-                                                                              Compara-                                           Example  tive Ex-  tive Ex-                                                                              tive Ex-                                           5        ample 1   ample 2 ample 3                                  ______________________________________                                        Salt spray                                                                              no       rusting of                                                                              rusting of                                                                            rusting of                               resistance                                                                              change   coating   coating coating                                  test.sup.1         from cut  from cut                                                                              from cut                                                    portion   portion portion                                  Adhesion test                                                                           63       40        25      43                                       (Kg/cm.sup.2).sup.2                                                           Weather resis-                                                                          no       partial   partial partial                                  tance test.sup.3                                                                        change   peeling at                                                                              peeling at                                                                            peeling at                                                  periphery periphery                                                                             periphery                                                   of cut    of cut  of cut                                                      portion   portion portion                                  Service water                                                                           40 days  18 days   10 days 22 days                                  dip resis-                                                                    tance test.sup.4                                                              Alkali resis-                                                                           no       partial   partial partial                                  tance test.sup.5                                                                        change   blistering                                                                              blistering                                                                            blistering                                                  and rusting                                                                             and rusting                                                                           and rusting                                                 on coating                                                                              on coating                                                                            on coating                               Acid resis-                                                                             no       partial   partial partial                                  tance test.sup.6                                                                        change   blistering                                                                              blistering                                                                            blistering                                                  and rusting                                                                             and rusting                                                                           and rusting                                                 on coating                                                                              on coating                                                                            on coating                               Humidity resis-                                                                         no       partial   partial partial                                  tance test.sup.7                                                                        change   blistering                                                                              blistering                                                                            blistering                                                  and rusting                                                                             and rusting                                                                           and rusting                                                 on coating                                                                              on coating                                                                            on coating                               Impact resis-                                                                           no       cracking  cracking                                                                              cracking                                 tance test.sup.8                                                                        change                                                              ______________________________________                                         Note                                                                          .sup.1 sequare cross cuts were formed in the coating and after 1000 hours     of salt spray, the coating was peeled and a check was made to determine       whether or not rusting had advanced below the coating from the cut portio     .sup.2 the coating was tested by a Tensilon tester and the strength per       cm.sup.2 necessary for breakage of the coating was measured                   .sup.3 cuts were formed in the coating, the coating was tested for 500        hours by a weatherometer, the coating was folded at an angle of 20.degree     and the state of the coating was examined                                     .sup.4 the sample was immersed in service water maintained at 60°      C. and the number of days for the appearance of any change in the coating     were recorded                                                                 .sup.5 the sample was immersed in a 5% aqueous solution of sodium             hydroxide for 5 months                                                        .sup.6 the sample was immersedin a 20% aqueous solution of hydrochloric       acid for 5 months?                                                            .sup.7 the sample was allowed to stand at a relative humidity of 100% for     1000 hours                                                                    .sup.8 the sample was tested by a Du Pont impact tester under conditions      of 1 Kg × 1/4"R × 50 cm                                      

EXAMPLE 6

    ______________________________________                                        Formula 9:                                                                    ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                        40     parts by weight                                   (Rigolac 150HR manufactured by                                                Showa High Polymer Co. Ltd.:                                                  Isophthalic acid type)                                                        Organic bentonite (Bentene #34                                                                     2.0    parts by weight                                   manufactured by National Lead                                                 Co. Ltd.)                                                                     Styrene              32.5   parts by weight                                   Cobalt naphthenate (containing                                                                     0.5    part by weight                                    6% of metallic cobalt)                                                        Glass flake (average particle                                                                      15     parts by weight                                   size = 150 to 200 microns,                                                    average thickness = 3 to 5 microns)                                           Scaly lead powder (manufactured                                                                    10     parts by weight                                   by Fukuda Metal Foil and Powder                                               Co. Ltd., average particle                                                    size = 150 to 200 microns,                                                    average thickness = 4 to 6 microns)                                           Total                100    parts by weight                                   Curing agents:                                                                Methylethyl ketone peroxide                                                                        0.2    part by weight                                    t-Butyl peroxyphthalate                                                                            0.6    part by weight                                    ______________________________________                                    

Among the main ingredients of formula 9, the unsaturated polyester resinwas first mixed with the organic bentonite, and the mixture was kneadedby a roller. Other ingredients were added to the kneaded mixture and themixture was stirred by a disperser to form a main ingredientcomposition. A soft steel plate (JIS G-3141) having a size of 150 mm×50mm×1.6 mm was subjected to shot blasting to remove mill scale, rest andoil completely. A paint formed by adding the curing agents to the mainingredient composition was air-spray-coated on this steel plate (the tipdiameter being 1 mm), so that the dry coating thickness was 500±50microns, and the coated steel plate was dried at 20° C. for 7 days andsubjected to comparison tests.

EXAMPLE 7

    ______________________________________                                        Formula 10:                                                                   ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                        35     parts by weight                                   (Rigolac LP-1 manufactured by                                                 Showa High Polymer Co. Ltd.:                                                  Bisphenol type)                                                               Organic bentonite (same as                                                                         3.0    parts by weight                                   used in Example 6)                                                            Paraffin wax         0.3    part by weight                                    Styrene              16.2   parts by weight                                   Cobalt naphthenate (same as                                                                        0.5    part by weight                                    used in Example 6)                                                            Glass flake (same as used in                                                                       15     parts by weight                                   Example 6)                                                                    Scaly zinc powder (manufactured                                                                    30     parts by weight                                   by Sakai Chemical Industries                                                  Co. Ltd., average particle                                                    size = 50 to 60 microns, average                                              thickness = 6 to 7 microns)                                                   Total                100    parts by weight                                   Curing agents:                                                                Methylethyl ketone peroxide                                                                        0.2    part by weight                                    Cumene hydroperoxide 0.3    part by weight                                    ______________________________________                                    

A coating composition of formula 10, formed by kneading in the samemanner as in Example 6, was coated on the same type of steel platesample as used in Example 6, and the coated steel plate was subjected tocomparison tests.

For reference, a photograph of the section of the coating obtained inthis Example, taken by using a scanning electron microscope, is shown inFIG. 4.

EXAMPLE 8

    ______________________________________                                        Formula 11:                                                                   ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                        40     parts by weight                                   (Repoxy R-800 manufactured by                                                 Showa High Polymer Co. Ltd.:                                                  Epoxy acrylate type)                                                          Organic bentonite (same as                                                                         1.0    part by weight                                    used in Example 6)                                                            Paraffin wax         0.3    part by weight -Styrene 28.2 parts by weight      Cobalt naphthenate (same as                                                                        0.5    part by weight                                    used in Example 6)                                                            Glass flake (same as used in                                                                       15     parts by weight                                   Example 6)                                                                    Scaly lead powder (same as used                                                                    20     parts by weight                                   in Example 6)                                                                 Total                100    parts by weight                                   Curing agents:                                                                Methylethyl ketone peroxide                                                                        0.2    part by weight                                    t-Butyl peroxyphthalate                                                                            0.3    part by weight                                    ______________________________________                                    

A coating composition of formula 11, formed by kneading in the samemanner as in Example 6, was coated on the same type of steel platesample as used in Example 6 so that the dry coating thickness was 500±50microns, and the coated steel plate sample was subjected to comparisontests.

EXAMPLE 9

    ______________________________________                                        Formula 12:                                                                   ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                        40     parts by weight                                   same as used in Example 6)                                                    Organic bentonite (same as                                                                         2.0    parts by weight                                   used in Example 6)                                                            Styrene              30.0   parts by weight                                   Cobalt naphthenate (contain-                                                                       0.5    part by weight                                    ing 6% of metallic cobalt)                                                    Glass flake (same as used in                                                                       20     parts by weight                                   Example 6)                                                                    Scaly lead powder (same as used                                                                    7.5    parts by weight                                   in Example 6)                                                                 Total                100    parts by weight                                   Curing agents:                                                                Methylethyl ketone peroxide                                                                        0.4    part by weight                                    Cumene hydroperoxide 0.7    part by weight                                    ______________________________________                                    

A coating composition of formula 12, formed by kneading in the samemanner as in Example 6, was airless-spray-coated on the same type ofsteel plate sample as used in Example 6 so that the dry coatingthickness was 500±50 microns (the tip diameter being 1 mm), and thecoated steel plate sample was dried at 5° C. and subjected to comparisontests.

EXAMPLE 10

    ______________________________________                                        Formula 13:                                                                   ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                        35     parts by weight                                   (same as used in Example 6)                                                   Organic bentonite (same as                                                                         3.0    parts by weight                                   used in Example 6)                                                            Paraffin wax         0.3    part by weight                                    Styrene              16.2   parts by weight                                   Cobalt naphthenate (same as                                                                        0.5    part by weight                                    used in Example 6)                                                            Glass flake (same as used in                                                                       20     parts by weight                                   Example 6)                                                                    Scaly zinc powder (same as used                                                                    25     parts by weight                                   in Example 7)                                                                 Total                100    parts by weight                                   Curing agents:                                                                Methylethyl ketone peroxide                                                                        0.4    part by weight                                    t-Butyl peroxyphthalate                                                                            0.8    part by weight                                    ______________________________________                                    

A coating composition of formula 13, formed by kneading in the samemanner as in Example 6, was airless-spray-coated on the same type ofsteel plate sample as used in Example 6 (the tip diameter being 1 mm) sothat the coating dry thickness was 500±50 microns, and the coated steelplate sample was dried at 5° C. and subjected to comparison tests.

COMPARATIVE EXAMPLE 4

    ______________________________________                                        Formula 14:                                                                   ______________________________________                                        Main ingredients:                                                             Unsaturated polyester resin                                                                       45     parts by weight                                    (same as used in Example 6)                                                   Organic bentonite (same as                                                                        2.5    parts by weight                                    used in Example 6)                                                            Styrene             26.7   parts by weight                                    Cobalt naphthenate (same as                                                                       0.8    part by weight                                     used in Example 6)                                                            Glass flake (same as used in                                                                      25     parts by weight                                    Example 6)                                                                    Total               100    parts by weight                                    Curing agent:                                                                 Methylethyl ketone peroxide                                                                       0.6    part by weight                                     ______________________________________                                    

A coating composition of formula 14, formed by kneading in the samemanner as in Example 6, was coated on the same type of steel platesample as used in Example 6 so that the dry coating thickness was 500±50microns, and the coated steel plate sample was dried at room temperaturefor 7 days and subjected to comparison tests.

The results of the comparison tests made on the coated steel platesamples obtained in the foregoing Examples and Comparative Example areshown in Table 2.

                  TABLE 2                                                         ______________________________________                                                    Example 6 Example 7 Example 8                                     ______________________________________                                        Salt spray resis-                                                                         no change no change no change                                     tance test                                                                    Adhesion test                                                                             65        58        60                                            (Kg/cm.sup.2)                                                                 Weather resistance                                                                        no change no change no change                                     test                                                                          Service water dip                                                                         40 days   39 days   40 days                                       resistance test                                                               Alkali resistance                                                                         no change no change no change                                     test                                                                          Acid resistance                                                                           "         "         "                                             test                                                                          Humidity resis-                                                                           "         "         "                                             tance test                                                                    Impact resistance                                                                         "         "         "                                             test                                                                          ______________________________________                                                                        Comparative                                               Example 9 Example 10                                                                              Example 4                                     ______________________________________                                        Salt spray resis-                                                                         no change no change rusting advanced                              tance test                      from cut portion                              Adhesion test                                                                             60        62        42                                            (Kg/cm.sup.2)                                                                 Weather resistance                                                                        no change no change partial peeling                               test                            at periphery of                                                               cut portion                                   Service water dip                                                                         45 days   50 days   21 days                                       resistance test                                                               Alkali resistance                                                                         no change no change partial blister-                              test                            ing and rust-                                                                 ing on coat-                                                                  ing                                           Acid resistance                                                                           "         "         partial blister-                              test                            ing and rust-                                                                 ing on coat-                                                                  ing                                           Humidity resis-                                                                           "         "         partial blister-                              tance test                      ing and rust-                                                                 ing on coat-                                                                  ing                                           Impact resistance                                                                         "         "         cracking                                      test                                                                          ______________________________________                                         Note                                                                          The test methods are the same as described in Table 1.                   

As will readily be understood from the test results shown in Tables 1and 2 and photographs shown in FIGS. 1 to 4, the coating film obtainedfrom the coating composition of the present invention according to thecoating process thereof is highly improved in corrosion resistance overthe coating films prepared from the conventional lining compositions,and the coating film obtained according to the present invention isexcellent in adhesion, impact resistance, weatherability and chemicalresistance. It will also be understood that these effects are attainedby synergistic actions of the unsaturated polyester resin and glassflake or the unsaturated polyester resin, glass flake and scaly metalpigment.

What is claimed is:
 1. A process for forming an anti-corrosive coatingon an iron or a steel substrate, which comprises mixing(i) 100 parts byweight of an unsaturated polyester resin containing an α,β-ethylenicallyunsaturated monomer, (ii) 10 to 70 parts by weight of glass flake havingan average particle size of 100 to 400 microns and an average thicknessof 0.5 to 5 microns, (iii) 10 to 150 parts by weight of a scaly metalpigment having particle size between 30-300 microns; (iv) 0.3 to 1.5parts by weight of curing promoter, then adding a member selected fromthe group consisting of (a) a mixture of 0.1 to 1.0 part by weight of aketone peroxide and 0.5 to 2.0 parts by weight of a hydroperoxide, (b) amixture of 0.1 to 1 part by weight of a ketone peroxide and 0.5 to 2parts by weight of a peroxy ester and (c) a mixture of 0.1 to 1.0 partsby weight of a ketone peroxide, 0.5 to 2 parts by weight of saidhydroperoxide and said peroxy ester, and spray coating to a coatingthickness of 300 to 1500 microns, by using a spray gun having a spraytip diameter of 0.5 to 3 mm.
 2. A process for forming an anti-corrosivecoating on an iron or a steel substrate according to claim 1, whereinsaid unsaturated polyester resin contains 10 to 50% by weight of anα-β-ethylenically unsaturated monomer.
 3. A process for forming ananti-corrosive coating on an iron or a steel substrate according toclaims 1 or 2 wherein said α,β-ethylenically unsaturated monomer isstyrene or methyl methacrylate.
 4. A process for forming ananti-corrosive coating for an iron or a steel substrate according toclaim 1 wherein the polyester resin is obtained by reacting an epoxyresin containing at least two epoxy groups per molecule with anα-β-monoethylenically unsaturated monocarboxylic acid.
 5. A process forforming an anti-corrosive coating on an iron or a steel substrateaccording to claim 1, wherein the average particle size of said scalymetal pigment is 30 to 300 microns and the average thickness is 3 to 10microns.
 6. A process for forming an anti-corrosive coating on an ironor a steel substrate according to claim 1 or 4, wherein said scaly metalpigment is a member selected from the group consisting of scaly leadpigment, scaly zinc pigment, scaly aluminum pigment, scaly stainlesspigment and scaly copper pigment.
 7. A process for forming ananti-corrosive coating on an iron or a steel substrate according toclaim 1, wherein said curing promoter is selected from the groupconsisting of cobalt naphthenate, copper naphthenate, calciumnaphthenate, barium naphthenate, zinc naphthenate and zirconiumnaphthenate.
 8. A process for forming an anti-corrosive coating on aniron or a steel substrate according to claims 1, 2 or 6 wherein saidspray-coating method is a compressed air spray or airless spray.